Method for data regeneration

ABSTRACT

A method for data regeneration of protected data is provided wherein an error rate of a reception signal with error correcting code is identified. A sampling time and a decision threshold are provisionally varied in a predetermined range until an optimum sampling time and an optimum decision threshold are recovered by identifying the transmission error during this procedure. As a result, additional transmission errors have no influence due to the error correction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for data regeneration ofprotected data wherein, based on error correction, a sampling time or asampling threshold may be provisionally shifted without having anerror-corrected output signal exhibit inadmissibly high data rates.

2. Description of the Prior Art

By comparing a sampled data signal to a data signal not yet sampled, acontrol criterion may be acquired that serves for the phase or/andfrequency readjustment of a clock generator. Such a phase detector isdescribed in IEEE, Journal of Lightwave Technology, Vol. LT-3, No. 6,pages 1312 through 1314. For extremely high data rates, smalldifferences in running time caused either by tolerances or bytemperature changes in the modules employed lead to the fact thatsignals are not sampled at an ideal point-in-time. Likewise, temperaturechanges can shift the sampling threshold, so that an optimum distinctionbetween, for example, two statuses no longer may be established. Aboveall, however, changes in the transmission pulse shape, influences of thetransmission path, pulse distortions of the reception side andasymmetrical influences on the two logical statuses transmitted preventthe definition of an optimum sampling threshold and of an optimumsampling time.

An object of the invention is to specify a method for optimum dataregeneration.

This object is achieved by the method recited in claim 1.

Advantageous developments are recited in the subclaims.

The method has the great advantage that, on the basis of the errorcorrection, it allows the sampling time or/and the sampling threshold tobe shifted provisionally without having the error-corrected outputsignal exhibit inadmissibly high data rates.

Just like the sampling time, the sampling threshold can be varied inorder to determine an optimum decision threshold.

SUMMARY OF THE INVENTION

Accordingly, in an embodiment of the present invention, a method isprovided for data regeneration which includes the steps of: acquiring acontrol criterion for a phase locked loop from a reception signal;generating a sampling clock signal; continuously monitoring atransmission error rate to control the phase locked loop; provisionallymodifying a controlled phase shift of the sampling clock signal comparedto the reception signal and, thus, the sampling time; and identifyingand setting an optimum sampling time based on the transmission errorrates measured at different sampling times.

In an embodiment of the method, the sampling time is set.

In an embodiment of the method, the sampling time is modified onlywithin a predetermined range.

In an embodiment of the method, the sampling time is only modified untila predetermined error rate is measured.

In an embodiment of the method, a provisionally set, new sampling timeis only retained when the error rate monitored for the new setting liesbelow the error rate of a preceding time interval.

In an embodiment of the method, following a modification of the samplingtime in only one direction, a lasting, new rated position is set whenthe measured error rate becomes lower.

In an embodiment of the method, the optimum sampling time is identifiedfrom the measured error rates only after a modification of the samplingtime in both directions and a resetting thereof is implemented.

In an embodiment of the method, the modification of the sampling timeoccurs by a predetermined amount.

In an embodiment of the method, the modification of the sampling time islimited to specific time spans.

In an embodiment, the method further includes the step of employing aplurality of interleaved codes for data protection, wherein the dataregeneration at a reception side occurs in different processing pathsand the transmission errors are separately identified, and wherein thesampling times are modified for only one of at least two data streams.

In an embodiment of the method, the sampling times are modified with theassistance of an adjustable delay element.

In an embodiment of the method, the sampling times are modified via acorrection voltage supplied to a controllable oscillator of the phaselocked loop.

In a further embodiment of the present invention, a method for dataregeneration is provided which includes the steps of: acquiring acontrol criterion for a phase locked loop from an encoded receptionsignal; generating a sampling clock signal; continuously monitoring atransmission error rate to control the phase locked loop; provisionallymodifying a decision threshold for the reception signal; and identifyingand setting an optimum decision threshold based on the transmissionerror rates given different decision thresholds.

In an embodiment of the method, the decision threshold is set.

In an embodiment of the method, the decision threshold is modified onlywithin a predetermined range.

In an embodiment of the method, the decision threshold is only modifieduntil a predetermined error rate is measured.

In an embodiment of the method, a provisionally set, new decisionthreshold is retained only when the error rate identified for a newsetting lies below the error rate of a preceding time interval.

In an embodiment of the method, following a modification of the decisionthreshold in only one direction, a lasting, new rated position is setwhen the measured error rate becomes lower.

In an embodiment of the method, the optimum decision threshold isidentified from the measured error rates only after a modification ofthe decision threshold in both directions and a resetting thereof isimplemented.

In an embodiment of the method, the modification of the decisionthreshold occurs by a predetermined amount.

In an embodiment of the method, the modification of the decisionthreshold is limited to specific time spans.

In an embodiment, the method further includes the step of employing aplurality of interleaved codes for data protection, wherein the dataregeneration at a reception side occurs in different processing pathsand the transmission error rates are separately identified, and whereinthe decision threshold is modified for only one of at least two datastreams.

When the identified error rate of the new sampling time setprovisionally lies above the error rate of the preceding sampling time,the previously employed sampling time (or the previously employedsampling threshold) is initially retained and a shift of the samplingtime in the other direction is provisionally implemented in order toidentify the optimum sampling time.

It is also advantageous that the sampling time and the samplingthreshold be adjusted only within a predetermined range. What is therebyassured is that the data regeneration still works even upon amalfunction of the control. Given interleaved error-correcting codes,the monitoring and readjustment of sampling time and sampling thresholdcan occur in different data paths, each of which are individuallyoptimized. This parallel processing is also required for technologicalreasons given high data rates. The other data path can serve ascomparison criterion. The ranges wherein the sampling time and thesampling threshold move can be determined from the previously measurederror rate and from the error rate occurring during the change.

It is also meaningful that, given a newly formed connection, the rangesfor readjustment of sampling time and sampling threshold, as well as thechange rate, are initially selected greater than given a connectionwhich already exists. It is advantageous in this method that no seconddata path need be provided, this serving only for determining theoptimum sampling time and the optimum sampling threshold that are thentransmitted on the actual data path. In this method, an optimum settingand data regeneration no longer can be achieved due to tolerances in thevarious data paths.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the Detailed Description of thePreferred Embodiments and the Drawing.

DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic circuit diagram associated with the method ofthe present invention.

FIG. 2 shows an alternative configuration of a schematic circuit digramassociated with the method of the present invention.

FIG. 3 shows another alternative configuration with separately protecteddata streams; and

FIG. 4 shows a time diagram associated with the method of the presentinvention.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS

FIG. 1 shows a schematic circuit diagram for implementing the method ofthe present invention. The transmitted data signal DS, including thecheck bits K serving the purpose of error correction, is supplied to adata input 1 of a decision stage ES. The output thereof is connected toa phase detector PD that contains an exclusive -OR gate EXOR foracquiring a control voltage that controls an oscillator VCO via a filterFI. This outputs a clock signal TS that, for sampling the received datasignal DS, K triggers a regenerator sampling trigger circuit KRconducted via an inverter IN or a delay element. The same clock signalTS is supplied via an adjustment delay element LZ and, as adjustablesampling signal TSV, triggers a sampling trigger circuit KA that outputsthe sampled data signal DS, K at its data output for further processing.The data signal DS-K is supplied to an FEC decoder that implements anerror recognition and/or error correction on the basis of the check bitsand outputs the corrected data signal DS at the data output 2. Givenboth high data rates and interleaved coding, a serial-to-parallelconverter can be inserted between the output of the sampling triggercircuit KA1 and the FEC decoder.

A control checks the transmission error rate at predetermined timeintervals on the basis of the correction frequency and, potentially,with an additional error recognition. These time intervals cancorrespond to a plurality of data blocks.

In order to set an optimum sampling time, the control provisionallymodifies the running time of the variable delay element LZ. Themodification of the running time corresponds to a shift of the samplingtime T_(A), which is only allowed to occur within a certain range BE.The deriving error rate can be employed as further limit, this alwayshaving to lie considerably below the error correctability of the codeemployed, but also being potentially dependent on the most recentlymeasured error rate.

The shift of the sampling time initially occur in one direction. Theerror rate is measured at the same time. When the error rate is reduced,the sampling time is shifted. This can occur by a fixed value; forexample, in that the provisionally implemented shift has lead to the newrated sampling time. When, by contrast, the error rate becomes higher, aprovisional shift occurs in the other direction, which first be precededby a further measurement in the previous rated position.

However, provisional shifts in both directions relative to the lastrated sampling time also be initially undertaken. The new sampling timeis determined on the basis of the measurements wherein the error rate isa minimum thereat. When a higher error rate than given the earliersampling time is to be anticipated given the new sampling time, nore-adjustment is implemented; rather, the error rate is initiallymeasured again in order to determine whether the transmission path has,potentially, become poorer.

The setting of the sampling time also can occur in very small, constantsteps; i.e., independent of the size of the identified deviation. Alocal minimum of the error rate must be avoided. At specific times orgiven newly connected connections, one can therefore initially beginwith larger provisional adjustments.

The control should include a low-pass function that only effects a finalshift of the sampling time after a considerable number of data blocks,when the newly identified sampling time is sure to lead to better errorrates. The number of setting events, also can be limited to specifictimes.

The sampling threshold can be set according to the same mode in that thecomparison voltage U_(AB) of the comparison stage VS is varied. Thecombination of the two measures effects an optimum regeneration of thereceived data signal.

The range BE in which a shift of the sampling time occurs and the rangeBA in which a shift of the decision threshold ES occurs can be limitedsuch that the error rate of the corrected data signal remains low as aresult of the search events, as shown in FIG. 4.

A delay element need not be employed for shifting the sampling time. Asshown in FIG. 2, the output of the comparison stage VS is directlyconnected to the input of the phase detector, to whose output the FECdecoder FEC-DEC is connected. The control ST influences the input of thecontrolled oscillator VCO here via an adder AD. The clock signal isshifted relative to the data signal due to the control criterion SKsuperimposed on the control signal RE. Separate comparison stages alsocan be employed for the sampling trigger circuit KA and the regeneratortrigger circuit KR.

In FIG. 3, a data signal DS, secured by error-correcting codesinterleaved with one another, and the respectively appertaining checkbits K are divided into two data streams. Two decision units VS1 and VS2are provided, each being followed by a sampling trigger circuit KA1 or,respectively, KA2. The trigger circuits are driven with clocks TS1 or,respectively, TS2 that are acquired by frequency division from the clocksignal TS. Each data stream DS1, DS2 is supplied to a separate FECdecoder FEC-DEC1 or, respectively, FEC-DEC2.

Both sampling clocks can be controlled via different delay elements LZ1and LZ2. The control varies the sampling time and the sampling thresholdfor, respectively, only one data path and implements an individualoptimization. There is the possibility of comparing the result not onlyto the preceding measured results but also to the measured results ofthe other data stream. Modified transmission conditions can, thus, betaken into consideration faster.

Although the present invention has been described with reference tospecific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the spirit and scopeof the invention as set forth in the hereafter appended claims.

What is claimed is:
 1. A method for data regeneration, comprising thesteps of: acquiring a control criterion for a phase locked loop from areception signal with error correcting code; generating a sampling clocksignal; continuously monitoring a transmission error rate to control thephase locked loop; provisionally modifying a controlled phase shift ofthe sampling clock signal compared to the reception signal with errorcorrecting code and, thus, modifying a sampling time; and identifyingand setting an optimum sampling time based on the transmission errorrates measured at different sampling times.
 2. A method for dataregeneration as claimed in claim 1, wherein the sampling time is set. 3.A method for data regeneration as claimed in claim 1, wherein thesampling time is modified only within a predetermined range.
 4. A methodfor data regeneration as claimed in claim 1, wherein the sampling timeis only modified until a predetermined error rate is measured.
 5. Amethod for data regeneration as claimed in claim 1, wherein aprovisionally set, new sampling time is only retained when the errorrate monitored for the new setting lies below the error rate of apreceding time interval.
 6. A method for data regeneration as claimed inclaim 1, wherein, following a modification of the sampling time in onlyone direction, a lasting, new rated position is set when the measurederror rate becomes lower.
 7. A method for data regeneration as claimedin claim 1, wherein the optimum sampling time is identified from themeasured error rates only after a modification of the sampling time inboth directions and a resetting thereof is implemented.
 8. A method fordata regeneration as claimed in claim 1, wherein the modification of thesampling time occurs by a predetermined amount.
 9. A method for dataregeneration as claimed in claim 1, wherein the modification of thesampling time is limited to specific time spans.
 10. A method for dataregeneration as claimed in claim 1, further comprising the step of:employing a plurality of interleaved codes for data protection, whereindata regeneration at a reception side occurs in different processingpaths and the transmission errors are separately identified, and whereinthe sampling times are modified for only one of at least two datastreams.
 11. A method for data regeneration as claimed in claim 1,wherein the sampling times are modified with the assistance of anadjustable delay element.
 12. A method for data regeneration as claimedin claim 1, wherein the sampling times are modified via a correctionvoltage supplied to a controllable oscillator of the phase locked loop.13. A method for data regeneration, comprising the steps of: acquiring acontrol criterion for a phase locked loop from a reception signal witherror correcting code; generating a sampling clock signal; continuouslymonitoring a transmission error rate to control the phase locked loop;provisionally modifying a decision threshold for the reception signalwith error correcting code; and identifying and setting an optimumdecision threshold based on the transmission error rates given differentdecision thresholds.
 14. A method for data regeneration as claimed inclaim 13, wherein the decision threshold is set.
 15. A method for dataregeneration as claimed in claim 13, wherein the decision threshold ismodified only within a predetermined range.
 16. A method for dataregeneration as claimed in claim 13, wherein the decision threshold isonly modified until a predetermined error rate is measured.
 17. A methodfor data regeneration as claimed in claim 13, wherein a provisionallyset, new decision threshold is retained only when the error rateidentified for a new setting lies below the error rate of a precedingtime interval.
 18. A method for data regeneration as claimed in claim13, wherein, following a modification of the decision threshold in onlyone direction, a lasting, new rated position is set when the measurederror rate becomes lower.
 19. A method for data regeneration as claimedin claim 13, wherein the optimum decision threshold is identified fromthe measured error rates only after a modification of the decisionthreshold in both directions and a resetting thereof is implemented. 20.A method for data regeneration as claimed in claim 13, wherein themodification of the decision threshold occurs by a predetermined amount.21. A method for data regeneration as claimed in claim 13, wherein themodification of the decision threshold is limited to specific timespans.
 22. A method for data regeneration as claimed in claim 13,further comprising the step of: employing a plurality of interleavedcodes for data protection, wherein data regeneration at a reception sideoccurs in different processing paths and the transmission errors areseparately identified, and wherein the decision threshold is modifiedfor only one of at least two data streams.